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Wednesday, 12 March 2014
14:15 - 15:45 Remote sensing: From toys to tools?
Resource Assessment  


Room: Tramuntana
Session description

The use of remote sensing within the wind industry has developed significantly since these techniques were first adopted. The new opportunities to make measurements that have been made available have themselves influenced the aims and objectives of the measurements, as it has become possible to consider assessing aspects of wind that were previously overlooked due to an inability to acquire data with more limited instruments. This has led to an industry-wide learning process, as new applications have emerged in response to the measurement opportunities made available by remote sensing, and more effective methods for meeting existing requirements of measurement campaigns have been identified. This session provides an opportunity both to review industry progress in making the most of remote sensing and to look ahead to the possiblities that are now emerging.

Lead Session Chair:
Peter Clive, SgurrEnergy Ltd, United Kingdom
Julia Gottschall Fraunhofer IWES, Germany
Co-authors:
Julia Gottschall (1) F P Tobias Klaas (1) Will Barker (2) Mike Harris (2)
(1) Fraunhofer IWES, Bremerhaven, Germany (2) ZephIR Ltd., Ledbury, United Kingdom

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Julia Gottschall (MSc, PhD) is a senior scientist and project manager at Fraunhofer IWES (Institute for Wind Energy Systems and System Technology) based in Bremerhaven / Germany. She obtained a PhD in applied physics from the University of Oldenburg and ForWind in 2009. From 2009 to 2011 she worked as a scientist at Risø DTU (now DTU Wind Energy) and specialized on power performance testing and lidar applications, contributing also to the revision of the IEC 61400-12-1 standard as a member of the MT12-1 committee. Her current research is focused on lidar measurements for wind resource assessment (onshore and offshore).

Abstract

Classification of remote sensing devices at different sites: a lidar case study

Introduction

The draft version of the IEC 61400-12-1 Ed.2 standard limits the application of remote sensing (and in particular lidar) devices to flat terrain. But it is expected that the devices will be applied at least for resource assessment campaigns also in more complex terrains without further corrections. Annex L of the draft includes verification and classification schemes for the estimation of measurement uncertainties in the final application of the device.
It is investigated how the results in flat and more complex terrain compare, and if additional testing in complex terrain may help to decrease the uncertainties in the final application.


Approach

Results from two measurement campaigns are evaluated and compared: a ZephIR 300 VAD-scanning wind lidar tested at the ZephIR Ltd. tall-mast site at Pershore, and a second lidar device of the same type next to the Fraunhofer IWES 200-m-meteorological mast at Rödeser Berg in moderately complex terrain. Both tests are evaluated in terms of a verification and classification of the remote sensing device for selected sectors. The influence of the environmental variables considered for the classification, as well as the interdependency between different variables is analysed and conclusions on the uncertainty budget for a final application at different sites are drawn.

Main body of abstract

The classification scheme outlined in the IEC 61400-12-1 Ed. 2 committee draft describes a procedure for determining the sensibilities of a remote sensing device on different external (environmental) variables. In principle, this procedure should ensure that the considered device can be applied at any site with a reasonably estimated associated uncertainty budget based on the extrapolated results of the verification and classification tests.
In the draft standard this concept is limited to flat terrain. But it is expected that it will be applied in the future at least for resource assessment campaigns also in more complex terrain.
In the present contribution we investigate how well the results for a lidar-mast comparison performed in flat terrain can be transferred to a moderately complex site. It is analysed how the deviations between lidar and reference mast measurements at the two sites compare and if they can be reconstructed on the basis of the systematic sensibilities to environmental variables found as results of the classification tests.
In particular, we want to answer the question if multi-site testing (including also the more complex sites for testing purposes, as e.g. the 200-m-mast test site at Rödeser Berg) may help to better estimate the uncertainties associated to the measurements of a remote sensing device, avoiding in particular an over-estimation of the components from a device classification due to the extrapolation of results from the test in flat terrain.


Conclusion

An understanding of the systematic sensibilities of lidar (or more generally remote sensing) measurements to the influence of environmental variables is critical for their application and a reasonable estimation of the associated uncertainties. This is particularly true when the variables cover a broader range during one application or when the overall environmental conditions are more complex. A detailed classification of a remote sensing device and multi-site testing, including different types of sites, may give a better understanding of the sensibilities and result in less conservative (more economic) uncertainty budgets.


Learning objectives
Delegates will learn how verification and classification tests for remote sensing devices are performed and evaluated, and how an uncertainty budget for the final application is estimated from the results. The conclusions from the presented study will enable them to arrange the tests in a way that may avoid unnecessarily conservative uncertainties and finally increase the value of their project.